Summary: Very nice lens for those times you aren't sure what you'll run into. It's not as fast as the rest of my glass, but it's a fine lens anyway. Quick, silent autofocus, easily adjustable friction control for the slide zoom. It's even positioned so that you can change it with one hand while holding the lens. The IS is good enough that you don't need a tripod even as slow as 1/60 or even a few stops slower.
Conclusion: I've got a number of lenses for my 5D Mark III - some from a 15 year old 30-D including a 28-200mm zoom. The old lens works on the Mark III just fine but really doesn't seem to provide the artistic effect that I wanted. So, I took the plunge and bought the EF 28-300mm IS USM lens. Boy, I am happy that I did! The new zoom lens is heavy to be sure and you'll probably want to hold the lens body as you carry it as it's a bit heavy for the neck strap alone.
Excerpt: The first day I used this lens for several hundred photos and every photo was usable. Since 2007 this lens has gone up in price and may increase in the near future. If you want versatility from 28 to 300 on a full frame or 400 plus on a crop this is the lens to invest in. Best quality L glass with IS 1 and 2 increasing 3 stops and auto focus at this price is amazing. The build quality to last and so far no dust or moisture problems in the lens.
Pros: Consistent Output, Durable, Easily Interchangeable, Fast / accurate auto-focus, Nice Bokeh, Rugged, Strong Construction
Excerpt: Captured an amazing images and easy to use. It was a heavy L Lens. But the weight was not an issue for me as long as I don't need to carry multiple cameras or lenses. This one does at all. Worked well with my M3 and 7D.
Pros: Consistent Output, Durable, Easily Interchangeable, Fast / accurate auto-focus, Strong Construction
Excerpt: I bought this lens after trying different all in one lens. It is simply the best lens out there. The disadvantage of it weight are over looked by the incredible pictures it takes. It is a must have lens.
Summary: Fabulous for an all purpose lens. I hate changing lenses and this gives you a ton of flexibility. It is a very heavy lens to tote around, but for me the advantage is that no one else in my family wants to use the camera.I've used the lens in extreme cold weather (-50 celsius) with no issues on a Canon 6D. I find that it's so rare that I'm shooting with a really low F stop on this lens that I'm glad that I didn't buy the Canon 200m zoom that's 2.8.
Conclusion: I have owned the lens for almost 3 years. I has performed admirably and has done everything that I have asked it to do. When used within its design range, you cannot have a better partner waiting on you to call it into action. I have never been disappointed with it. Some comment that it is heavy. It is only 8 oz. heavier that the 70-200 F2.8 and no one complains about that one. I have carried it afield on numerous occasions and have not been made weary from the weight.
Pros: Fast auto-focus, Superior build quality, Super-sharp images